1. Field of the Invention
The present invention relates to an image processing method and an image processing apparatus for carrying out image processing on image data that have already been subjected to image processing carried out by a digital camera or the like and added with image processing information regarding the image processing by the digital camera or the like. The present invention also relates to a program embodied on a computer-readable recording medium to cause a computer to execute the image processing method.
2. Description of the Related Art
In a digital still camera (hereinafter referred to as a digital camera), an image obtained by photography can be recorded as digital image data in a recording medium such as an internal memory or an IC card, and can be reproduced by a printer or a monitor based on the digital image data. In the case where an image obtained by a digital camera is reproduced, the image is expected to have as high a quality as a print generated from a negative film.
When a print is generated in the above manner, the quality of the print can be improved by carrying out thereon image processing such as density conversion processing, white balance processing, gradation conversion processing, saturation enhancement processing, and sharpness processing. Therefore, a method has been proposed (U.S. Pat. No. 6,011,547), in order to obtain high-quality printed matter. In this method, photography information such as information on use of flash and the type of lighting is added to image data obtained by a digital camera, and more appropriate image processing can be carried out on the image data with reference to the photography information added to the image data.
Meanwhile, a digital camera has also been proposed that enables output of photographed image data having been subjected to automatic or manual image processing. In such a digital camera having an image processing function, image processing is carried out so as to attain an optimal image quality according to a photographed scene and a photography condition. Furthermore, a photographer can select the type of image processing to be carried out on the image data and various functions related to the image processing according to his/her intention. For example, automatic white balance processing, white balance processing in a fixed light source mode, processing for image quality modification (regarding tones, sharpness, and chroma) and a preference regarding reproduced image (such as preference for a monochrome image, a sepia-color image, and a beautiful skin color) can be selected as the type of image processing. As the various kinds of functions regarding image processing are included selection of a photography mode (such as portrait mode, scenery/distant view mode, macro/close-up mode, night view/fireworks mode, underwater photography mode, and user exposure correction mode), an automatic bracket function, photography using an optical filter, soft focus photography, interval photography, serial photography, multiple exposure, superposition with a template, and superposition with a frame. Optimal image processing can be carried out, reflecting an intention of the photographer according to the selected type of image processing and function.
In the case where image data obtained by such a digital camera having an image processing function are reproduced by a reproduction apparatus such as a printer or a monitor, further image processing is carried out on the image data. However, if the image processing is further carried out on the image data that have already been subjected to the image processing by the digital camera, a reproduced image may not have the quality intended for by the digital camera or the reproduction apparatus.
Meanwhile, automatic white balance processing by a digital camera refers to processing that causes white balance of an image photographed in artificial lighting to look like white balance of an image photographed in daylight. More specifically, the automatic white balance processing is to correct image data so as to cause an average of the image data (that may exclude high saturation pixels) to become a gray value having an intended color temperature (such as color temperature of daylight or tungsten light). For this reason, when automatic white balance processing is carried out, an image photographed in a light source having a low color temperature such as a tungsten light can be reproduced to have more preferable or natural colors. If a sunset is photographed in a fixed daylight mode among fixed light source modes of a digital camera, image data processed by the automatic white balance function enables reproduction of an image reflecting a reddish color of the sunset.
On the other hand, in a reproduction apparatus, white balance processing is carried out for absorbing a characteristic of white balance of a digital camera. Therefore, images obtained from a reproduction apparatus have almost the same white balance, since the reproduction apparatus cannot distinguish between automatic white balance processing set in a digital camera and image processing in a fixed light source mode.